PROJECT SUMMARY/ABSTRACT The performance of many x-ray imaging systems is limited by the lack of x-ray detectors with simultaneous high quantum efficiency and high spatial resolution. As examples, digital mammography scanners typically have a resolution of ? 70 m for high quantum efficiency, which is not sufficient to effectively detect small but critical microcalcifications. X-ray micro-CT scanners either use high quantum efficiency, low spatial resolution detectors together with high geometric magnification or use high spatial resolution, low quantum efficiency detectors with thin scintillators, which significantly limits the scan throughput. The low-resolution (typically ~ 100 m) of commercial large area x-ray flat panel detectors made single-shot x-ray phase contrast imaging system not appropriate for most applications since the resolution is determined by the fringe period and has to be at least a few pixels. Research in pixelated scintillators during the last two decades have demonstrated pixel size determined spatial resolution. However, the light guiding (output) efficiency is very low (typically < 10%), which limits the practical application of such detectors in low dose medical x-ray diagnosis. The proposed research in this SBIR Phase I project will focus on developing high light guiding efficiency pixelated scintillators with specially designed and engineered sidewall surface reflectors of the pixels. The spatial resolution defined by the pixel size (down to 15 m) and the light guiding efficiency comparable to commercial phosphor screens of the same thickness are to be demonstrated. General Optics proposes to bring such high efficiency pixelated scintillators to the market through Phase I research. The specific aims are: (1) develop processes to fabricate 30-m and 15-m pitch, up to 200 m depth silicon pixel wells with ? 1 m wall thickness, and engineer the sidewall surface for high reflectivity; (2) fill the wells with scintillator materials of CsI (Tl) and Gd2O2S:Tb; (3) Test the performance of the fabricated pixelated scintillators and compare them with commercial phosphor screens. Integration of the pixelated scintillators to large area CMOS cameras for fully integrated, large area x-ray detectors would be the next stage of this SBIR Phase I project.